Innovative synthesis of citrate-coated superparamagnetic Fe3O4 nanoparticles and its preliminary applications

► An effective route for citrate coated Fe3O4-based MR contrast agent. ► A relatively higher longitudinal relaxivity (r1) and lowest relaxivity ratio (r2/r1). ► In vitro studies show both phagocitic and non-phagocytic uptake of these nanoparticles. ► In vivo MR imaging of swine head and spine tissues show both T1 and T2 contrast effect.